I'm playing mine from my External HDD and I experienced no lag, but it did freeze a lot. I guess you can try playing it from the External HDD and see what happens, many people also said that they experienced lag so it is common.

I did so:
1) extracted actor33.psarc
2) replaced only original u2-journal-lod0.pak into actor33 folder with one coming from Uncharted.3.PROPER.FIX.KMEAW355.READNFO.v4-Nobody patch
3) deleted original actor33.psarc (you have the actor33 folder now )
4) deleted camera.txt from movies1 folder
5) replaced eboot.bin

I hope this can be useful to people have still problems with this awesome game.